Guitarriasta that is a good diagram to show that tuning a piano is a bit too complicated for your average player .That diagram showed how a very expert tuner would do it . The history said that there became a separation of players and tuners . Players rarely tuned their own pianos . So tuners must have had the biggest influence on what tuning system was used . They knew the black arts .Players just had to trust them .Nowadays there is quite a lot of resistance by tuners to unusual (Not ET) tuning and some tuners would be a bit mystified to change their methods . My piano tuner converted our piano to Kirnberger III but he used an electronic tuner. He was impressed by some Debussy that he knew . It was his first taste of unequal tuning .
Comparing different instruments for a second. A Piano can be converted to any historical tuning but still needs regular attention . A violin ,viola or cello in the right hands can sound more accurately in tune than a guitar or piano ,due to player skill . The way I see it now , a guitar with altered frets ,in a historical temperament ,can be dead accurate as soon as the 6 strings are tuned. That puts it ahead of the piano for ease of tuning . It also puts bowed fretless instruments in second place because the tuning will automatically play accurately . The only slight drawback ( or major obstacle --your choice ) is a guitarist worrying about out of line frets . How many worry about that when they have never tried it ? It`s worth it just to be one up on violinists .
Here`s a perspective on that . Imagine that all pianos were made with just a straight row of white keys . After a number of years a new style of keyboard arrives with black keys ,out of line , and not looking so pretty . Uproar from the players . "How can we play that ? " they shout .
Once you try the first attempt at placing out of line frets to get the temperament , you then need to work out how to minimise the "out of lineness". The bridge ,nut and even the string lengths can be adjusted . If you can bear that disruption the frets will at least line up on the most important 12 th fret . The best way to test this is to start with a cheap guitar . There must be some in the world . They can be a big help . You could glue on ebony strips that were made for bindings . No worries about glues etc .No cutting of grooves needed . The ebony will last long enough to let you hear the temperament you have chosen .
Fret levelling will be easy for the first attempts . A Korg Orchestral Tuner is a good guide for this .The temperaments are programmed in . [ Not written to annoy anybody .]

Ah, but after you level the frets you have to round off the tops. A fret with a flat top can cause a sitar-like buzz. Rounding is generally done with a file of some sort. Stepped frets could be very hard to round over, unless they're done like croquet hoops so that you could get in between.

The curiosity is killing me. When someone has absolute pitch or perfect pitch, which temperament are they tuned to?

Perfect pitch is a curse. When sense of pitch is too good one always suffers from feeling any instrument or temperament out of tune. Even thirds feel dissonant, only forths, fifths and octaves sound perfect.

I've heard about a guy with perfect pitch who could not play or listen to any instrument except bells tuned to perfect 4ths, 5ths and 8ths.

I don't know if my pitch is perfect but yet there are days when it gets more acute and I'm just not able to tune the guitar to be in tune all across the fretboard so I have to stop playing.

Fret levelling ,if you want to use ebony .You can shape the top of the fret before fitting it. That will not be a major problem . A man of your callipers should be able to manage that . I used 2mm thick brass (circular section) with conrtact glue that allowed time for adjustments before it set . It`s very reliable . It`s not attractive but can be cleaned up later.
The question I asked earlier about Eben Goresko and what he meant about ET not being possible before the 20 th century might be connected with the 1917 book by William Braid White ."Modern Piano Tuning and Allied Arts". It discusses ET thoroughly and is free to read online . One quote is about the original keyboard being used in the 14th century and shows the "Slowness of the human mind and it`s hatred of change ". I wonder if that`s true .It`s on page 73 in case anyone doesn`t believe me . In 1917 he tells us the pitch standard was 435. See Page 76 .
On Page 81 "---of course as the manufacture of pianos and organs is stressed rather on it`s industrial rather than on it`s artistic side we shall probably have to remain content with Equal Tuning ." Howard Goodall needs to see that .
At that time they had developed ways to measure frequency accurately and combined with this book it seems to tidy up the subject . With the charts in the book they had what was needed to take the guesswork out of ET .
The Pro Audio Encyclopedia has a relevant page under "History of Audio and Sound Measurement ". That mentions technical advances made around 1917 which would have combined with the W.B.White book .

I hope I live to see equal temperament tuning represented by computer generated graphics (in Colorado please).

Not sure what you mean.

I'd love to see a graphic which shows you how far "out of tune" the guitar fretboard is when you:
- tune it to different temperaments.
- play in different keys in the above temperaments.
- play different intervals in the above temperaments.
- (and of course move the frets...)

I'd love to see a graphic which shows you how far "out of tune" the guitar fretboard is

I don't think the graphics would be hard to do. The problem is defining what "out of tune" means. What is the reference?

I believe there is such a thing as perfect tuning for any given note but I do not think it is traditional just intonation and nobody thinks it is a tempered tuning system (nobody who thinks there is such a thing as perfect tuning, that is).

Some violinists will play scales in a different intonation than arpeggios - or at least the thirds of arpeggios. I think that is the right approach, but it makes it much more complicated to figure out what the reference pitch is.

I think there is a table on Wikipedia comparing ET to a system of just intonation, which does give some guide even if (as I believe) traditional just intonation is not really the right comparator.

I find this stuff interesting, but at the same time the ear has some tolerance and we get to a point where we are obsessing over stuff that doesn't really matter.

I'd love to see a graphic which shows you how far "out of tune" the guitar fretboard is when you:
- tune it to different temperaments.
- play in different keys in the above temperaments.
- play different intervals in the above temperaments.
- (and of course move the frets...)

Pretty hard to do on just one static graphic, but here's a slide I use in one of my teaching presentations. It compares the sizes of the scale intervals when playing Just temperament in key, just temperament massively out of key and equal temperament. If you can get a guitar to play equal temperament accurately (most don't) I find the resulting "in-tuneness" will satisfy the vast majority of people.

Just vs. Equal.jpg

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With devices now available that tune the guitar for you (like the Roadie gadget being discussed in another thread, or the one Gibson fits to its electrics) it would be possible to have a JT guitar with curved frets that could move between a few keys in a matter of a second or so. It is probably not beyond the wit of man to come up with frets with curves that could also be varied automatically, opening up the other keys. I doubt there would be much of a market though.

The graphic is interesting. People take in information in different ways but to me it is easier to say "in ET the thirds of all the major chords are a bit sharp, but it works for all keys, unlike JI which sounds terrible if you go far round the circle of fifths from the home key.

String bending is obviously difficult on CG because you have to move the string a lot further to get the same change in pitch that you would on a steel string. When you bend a string, you actually increase its effective length, which would cause the pitch to fall, but on a steel string this effect is massively outweighed by the increase in tension and the pitch rises. On CG it might be possible to put waves in the fret, a bit like this ~~~~~~~ so that if the note you were fretting was the major third of a chord, you could drop it in pitch slightly by pushing or pulling the string across the fretboard, without the drop being outweighed by the increase in tension. Sometimes that would be harder to do than others, but the chord would still sound OK.

Or maybe CG is already difficult enough.

I would be interested enough to try something like that, but overall I am happy with the tuning and intonation on my standard guitar. I sometimes feel there is a subtext to posts on this topic that goes "superior musician, more sensitive to tuning, less receptive to ET; inferior musician, less sensitive to tuning, more receptive to ET", or "if you don't agree with me it's because your ears aren't good enough". If so, I protest. You can be aware that something is a compromise and still think it is one worth making, and many fine musicians have chosen fixed pitch instruments and dealt with the problems they bring rather than choosing a string instrument.

I don`t like Equal Temperament .Nothing to do with other people .I hate cabbage too . But I don`t feel superior to people who like cabbage . The Young temperament would be a good one for guitars . By the way if you tot up all the guitar music written in their keys you get a majority in simpler keys with fewer sharps /flats .That would give you more pure (natural ) tuned sounds .That`s the most useful comment ever made on this forum . Even better than the last one .

What I mean is I imagine a computer generated animated graphic that represents sound waves in motion and in color.
The waves would be a certain color when on equal temperament and gradually change color.

What, for example, would moving sound waves look like if the octave were blue, the fifth red, and all the way down the line. Surely there must be a better way to graphically represent sound waves than the hokey 2 dimensional drawings we seem to be stuck on.

I'm thinking of companies like Tableau Software that are at the forefront of the Big Data revolution. On their website you can see video examples of how data is animated graphically in real time. Why not do something similar in music?